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Techniques for Fracture Toughness Testing of Offshore Pipelines

[+] Author Affiliations
Andrea Fonzo, Giorgio Melis

Centro Sviluppo Materiali SpA, Pula (CA), Italy

Luigi Di Vito, Gianluca Mannucci

Centro Sviluppo Materiali SpA, Rome, Italy

Philippe Darcis, Gilles Richard, Hector Quintanilla

TenarisTamsa, Veracruz, México

Mariano Armengol

TenarisDalmine, Dalmine (BG), Italy

Paper No. OMAE2009-80135, pp. 249-257; 9 pages
doi:10.1115/OMAE2009-80135
From:
  • ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering
  • Volume 6: Materials Technology; C.C. Mei Symposium on Wave Mechanics and Hydrodynamics; Offshore Measurement and Data Interpretation
  • Honolulu, Hawaii, USA, May 31–June 5, 2009
  • Conference Sponsors: Ocean, Offshore and Arctic Engineering Division
  • ISBN: 978-0-7918-4346-8 | eISBN: 978-0-7918-3844-0
  • Copyright © 2009 by ASME

abstract

The need to evaluate the significance of flaws in welded pipelines for gas transportation requires the knowledge of the material resistance to ductile tearing. In particular, the fracture resistance of pipe girth welds should be evaluated since they may potentially be critical for structural integrity. Standard toughness Three Point Bending tests (SENB) are too conservative since they are more constrained than actual pipeline. In this case, the adoption of a reduced notch depth, which is considered to reproduce well actual stress-strain conditions at the crack tip of a weld flaw, increases critical toughness values when compared to standard specimen configuration. Alternative solutions may be applied, even if not yet included in toughness standards. In particular, the Single Edge Notch Tensile (SENT) test is a possible solution reducing conservatism. A matter of concern for toughness characterization of weld joint is also represented by the notch orientation, since the weld microstructure is inhomogeneous in nature. The L–R oriented specimen (notch at the pipe inner surface) typically shows CTOD values strongly lower than the ones of L–T oriented specimens (through thickness notch) for both weld metal and heat affected zone. All these issues are discussed within this paper, while an advanced approach is presented to determine the resistance curve by using a single SENT specimen with the compliance method for crack growth evaluation. A relationship between the specimen elastic compliance and actual crack growth was determined through Finite Element Analysis and a Fracture Mechanics model. Such a relationship is presented and compared to other solutions available in scientific literature.

Copyright © 2009 by ASME

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